Electrical components for interconnection systems, such as contacts or relays, are usually manufactured from copper or a copper alloy for high electrical conductivity. A protective coating is usually used to prevent copper oxidation. Copper oxidation is detrimental since copper oxide will increase the contact resistance of the component. One widely used protective coating is gold. Tin and palladium alloys are also widely used. For example, palladium alloys for connector applications are disclosed in a paper by Lees et al, presented at the Twenty Third Annual Connector and Interconnection Technology Symposium and include palladium/25% by weight nickel and palladium/40% by weight silver. Ternary alloys such as palladium/40% silver/5% nickel are also utilized.
Silver coatings have also been used to improve conductivity and provide corrosion resistance as disclosed in U.S. Pat. No. 4,189,204 to Brown .RTM.t al. The use of silver as a coating for connector contacts has been limited. Silver is characterized by poor sulfidation resistance and low hardness. However, silver has advantages over gold and a need exists for a reliable silver coating for electrical connector applications. Silver is comparatively inexpensive relative to gold and has high electrical conductivity. The metal is easily deposited by electrolytic means.
When silver has been used as a coating material, The coating was usually electrolytically deposited to a thicknesses of from about 1 to about 2.5 microns (about 40-1? microinches). Silver clads having a thickness in excess of about 25 microns have also been employed. These two thickness characteristics have generally been unacceptable because at the lower limits, the low hardness of silver leads to erosion to the base metal. At the higher thicknesses, both the weight and the cost of the silver become detrimental.